eventcv_core/transform/
algebra.rs

1//! Polarity and stream-algebra transforms — filtering, reordering and combining streams.
2
3use crate::{EventStream, EventStreamBuilder};
4
5impl EventStream {
6    /// Keeps only events of the given polarity.
7    pub fn filter_polarity(&self, polarity: bool) -> EventStream {
8        let (width, height) = self.sensor_size();
9        self.remap(width, height, |x, y, t, p| {
10            (p == polarity).then_some((x, y, t, p))
11        })
12    }
13
14    /// Flips every event's polarity. Sensor and timestamps unchanged.
15    pub fn invert_polarity(&self) -> EventStream {
16        let (width, height) = self.sensor_size();
17        self.map_columns(width, height, |out| {
18            for p in &mut out.ps {
19                *p = !*p;
20            }
21        })
22    }
23
24    /// Returns a copy reordered by ascending timestamp (stable for equal timestamps).
25    pub fn sort_by_time(&self) -> EventStream {
26        let (width, height) = self.sensor_size();
27        let ts = self.ts();
28        let mut order: Vec<usize> = (0..self.len()).collect();
29        order.sort_by_key(|&index| ts[index]); // stable
30        let (xs, ys, ps) = (self.xs(), self.ys(), self.ps());
31        let mut builder =
32            EventStreamBuilder::with_capacity(width, height, self.timestamp_scale_ms(), self.len());
33        for index in order {
34            builder.push(xs[index], ys[index], ts[index], ps[index]);
35        }
36        builder.build()
37    }
38
39    /// Concatenates several streams into one (in argument order, not time-sorted). The sensor
40    /// size is the element-wise maximum of the inputs; the timestamp scale comes from `self`.
41    pub fn concat(&self, others: &[&EventStream]) -> EventStream {
42        let (mut width, mut height) = self.sensor_size();
43        for other in others {
44            let (w, h) = other.sensor_size();
45            width = width.max(w);
46            height = height.max(h);
47        }
48        let total = self.len() + others.iter().map(|s| s.len()).sum::<usize>();
49        let mut builder =
50            EventStreamBuilder::with_capacity(width, height, self.timestamp_scale_ms(), total);
51        for stream in std::iter::once(self).chain(others.iter().copied()) {
52            builder.extend_from_stream(stream);
53        }
54        builder.build()
55    }
56}
57
58#[cfg(test)]
59mod tests {
60    use crate::{EventStream, EventStreamBuilder};
61
62    fn sample() -> EventStream {
63        let mut builder = EventStreamBuilder::new(4, 3, 0.001);
64        builder.push(0, 0, 30, true);
65        builder.push(1, 1, 10, false);
66        builder.push(2, 2, 20, true);
67        builder.build()
68    }
69
70    #[test]
71    fn filter_polarity_splits_and_conserves_count() {
72        let s = sample();
73        let on = s.filter_polarity(true);
74        let off = s.filter_polarity(false);
75        assert_eq!(on.len() + off.len(), s.len());
76        assert!(on.ps().iter().all(|&p| p));
77        assert!(off.ps().iter().all(|&p| !p));
78    }
79
80    #[test]
81    fn invert_polarity_is_its_own_inverse() {
82        let s = sample();
83        assert_eq!(s.invert_polarity().invert_polarity().ps(), s.ps());
84        assert_eq!(s.invert_polarity().ps(), &[false, true, false]);
85    }
86
87    #[test]
88    fn sort_by_time_orders_ascending() {
89        let sorted = sample().sort_by_time();
90        assert_eq!(sorted.ts(), &[10, 20, 30]);
91        assert_eq!(sorted.xs(), &[1, 2, 0]); // rows follow their timestamps
92    }
93
94    #[test]
95    fn concat_appends_and_takes_max_sensor() {
96        let a = sample();
97        let mut b_builder = EventStreamBuilder::new(8, 6, 0.001);
98        b_builder.push(7, 5, 50, true);
99        let b = b_builder.build();
100
101        let combined = a.concat(&[&b]);
102        assert_eq!(combined.len(), 4);
103        assert_eq!(combined.sensor_size(), (8, 6)); // element-wise max
104        assert_eq!(combined.ts(), &[30, 10, 20, 50]); // argument order, not sorted
105    }
106
107    #[test]
108    fn algebra_ops_handle_empty() {
109        let empty = EventStreamBuilder::new(4, 3, 0.001).build();
110        assert!(empty.filter_polarity(true).is_empty());
111        assert!(empty.sort_by_time().is_empty());
112        assert_eq!(empty.concat(&[&sample()]).len(), 3);
113    }
114}
eventcv_core/transform/algebra.rs

eventcv_core/transform/
algebra.rs
